1. Field of the Invention
The present invention relates generally to retractable seal double-block and bleed plug valves and more specifically to plug valves of that type in which the plug is designed to be self-supporting thereby obviating the usual requirement for supporting the plug by means of a trunnion and bushings.
2. Prior Art
Double block and bleed plug valves are well known in the art as exemplified by U.S. Pat. No. 3,011,513 issued to Heinen in 1961. Their positive sealing and superior flow characteristics are high advantageous for controlling the flow of fluids. Plug-type valves are generally the type in which a valve body is provided with a pair of axially aligned ports which are connected to incoming and outgoing fluid lines for movement of the fluid under pressure therethrough. Typically, a plug is adapted to selectively rotate within the main chamber of the valve to either provide a continuous channel between the incoming and outgoing coaxial ports when the valve is in the open position or a fluid-tight seal in one or both of the coaxial interconnecting ports when the valve is in the closed position.
Heinen discloses a centrally located cylindrical plug disposed within the valve chamber and provided with an upwardly extending shaft or trunnion which extends through the upper portion of the valve body and a downwardly extending shaft or trunnion which is received and terminates within the bottom plate of the valve body. As is well-known in the art, such trunnions assure the coaxial stability of the rotatable plug while also permitting vertical motion of the plug to allow seating and unseating of the valve slips as a result of the interaction of tapered flat surfaces of the plug and the slips.
The plugs of such valves are generally supporting by means of bushings which are in turn supported by the valve bonnet and lower plate. The bushings support the plug by means of the trunnions which extend above and below the plug. Unfortunately, the presence of a lower trunnion in particular makes it impossible to provide a flat lower body plate, thereby requiring an increased size in the overall valve body. Furthermore in such conventional plug type valves, the position of the plug within the body is dictated by the position of the trunnions which, int urn, is dictated by the locations of the bushings which are, in turn, dictated by the positions of the bonnet and lower plate which are all, in turn, dictated by the shape of the body. Consequently, plug location is not always possible to optimize for efficient valve operation.
Furthermore, the conventional design of plug type valves requires that the stem or trunnion be structurally stiff in order to support tremendous side loads and that they be hardfaced in order to withstand the engagement with a bearing surface. Furthermore, the bonnet and lower plate of the valve body must be relatively thick in order to provide significant structural support for the upper and lower bushings respectively, both of which must bear a substantial side load, particularly when the valve is in the closed position.
Clearly from the above noted disadvantages, it would be highly desirable to provide a self-supporting plug which obviates the requirement of conventional plug type valves for being supported by separate bushings, a lower trunnion and larger, heavier body members, all of which make the valve larger and more cumbersome and more expensive.
Relevant prior art known to the applicants includes the following:
66,657, Westlake;
178,312, Leland;
223,486, Cushing;
249,046, Hilliard;
370,780, Grossman;
452,188, Moore;
543,693, Keyes;
558,708, Baldwin;
565,730, Foote;
580,940, Hambleton;
615,616, Glauber;
745,316, Blake;
931,155, Smith;
1,572,678, Pordon.
U.S. Pat. No. 223,486 to Cushing is directed to what is termed a stop-cock. A plug B seats within a body A. A nut C acts as a bushing to hold the shoulder A.
U.S. Pat. No. 178,312 to Leland is directed to a combined stop-cock and T-joint. A plug D interfaces with the body.
U.S. Pat. No. 615,616 to Blauber is directed to a mechanism for securing washers on plug valves. A plug B interfaces with a casing A.
U.S. Pat. No. 452,188 to Moore is directed to a faucet type valve system and provides for a direct interface of the plug with a main body. The bottom portion may constitute a bushing F in the form of a washer.
There is apparently no prior art disclosure of a double block and bleed plug valve of the type shown in the Heinen patent and which employs a self-supporting plug to obviate a lower trunnion and bushings to bear the side loads.